A. Field of the Invention
This invention relates generally to dashpot assemblies and more specifically to dashpot assemblies used for damping the movement of poppets.
B. Background Art
A problem common to solenoid actuated poppet valves is obtaining proper response to the pressure actuating force to produce the desired control of fluid. Too slow or too fast movement responsive to the applied pressure may result in uncontrolled oscillation, chatter, and generally unacceptable performance. More particularly, poppet valves provide quick opening and closing times but produce rapid fluid changes, which in turn produce abrupt displacement of a mass or load downstream of the valve seat. This abrupt displacement may cause damage to the mass being displaced.
In some applications it is desirable to damp the opening of a valve orifice but permit its rapid closing. As shown, for example, in U.S. Pat. No. 4,202,250, a dashpot assembly controls the movement of a normally closed poppet. When actuated to open, the dashpot is effective to damp the opening of the valve orifice by damping the movement of the poppet. However, when actuated to close, the dashpot permits rapid closing of the orifice.
In some applications the reverse may be desirable. That is, it may be desirable to damp the closing of an orifice but permit its rapid opening. As an example, in an agricultural combine having a heavy header and springy tires, a normally open poppet is actuated to a closed state to start raising the header, but is actuated to the normally open state to stop raising the header. Accordingly, the starting movement of the header must be damped to prevent start shock. On the other hand, once the header reaches to desired height, overshoot must be prevented by rapidly stopping the raising.
Therefore, an object of this invention is to provide a dashpot assembly for damping the movement of a poppet during its actuation to the closed state, but to provide an undamped movement during its actuation back to its open state.